The present invention relates to a method of detecting a surface defect or flaw of metallic material, and specifically a method of detecting designed to carry out high precision detection of the depth of a surface defect or flaw of metallic material at any temperature.
Generally, various sorts of surface defects or flaws take shape in the manufacturing processes of metallic material. The surface flaws of these sorts are what must be detected and removed in a proper manner.
Given below will be a statement of surface flaws taking shape on iron and steel members constituting a sort of metallic material. In general practice, intermediate products of such iron and steel members as billets, blooms, slabs and the like are manufactured in the iron and steel manufacturing processes through a continuous casting process or a blooming or slabbing process. These intermediate products of iron and steel members have various shapes and various depths of surface flaws caused during in the course of the manufacturing processes.
In the conventional practice, each one of the above-mentioned iron and steel members manufactured by either a continuously casting apparatus or a blooming apparatus is subjected to cooling down to the normal temperature level, and then an inspection of whether or not surface flaws are present is conducted. Surface flaws, if any, are removed, and reheating is conducted, then the iron or steel member is properly rolled into a finished product, such as a steel plate, a hoop, a strip steel member, or the like.
The said intermediate products of iron and steel members of the normal temperature level have surface flaws removed by such means as melting and/or grinding, when the surface flaws are detected directly through visual inspection by an inspecting worker or when information with regard to the presence and the position of the flaws is given by such a surface flaw detection system as detects the presence of surface flaws of the iron and steel members and the positions of the surface flaws of the iron and steel members. However, the visual inspection by an inspecting worker has proved that measurement of the depth of a flaw is not practicable, and mere location of the presence of a flaw has been conducted. Even the said surface flaw detection system could only obtain information with regard to the presence and the position of the flaw, and it was not possible to obtain information with regard to the depth of the flaw. For this reason, in the flaw removal processes of scarfing and grinding, surface flaws have been removed in a manner of repeating the trial-and-error method wherein a melting workman and a grinding workman conducted scarfing and grinding to such depth and over such an area as were regarded intuitively by them to be appropriate. The scarfing workman and the grinding then workman conducted inspection once again thereafter with regard to whether or not the flaws had been removed. If some flaws remain untreated, the scarfing and grinding processes were repeated. On the other hand, in the case of introducing an apparatus for automatically removing surface flaws and combining the same with the above-mentioned surface flaw detection system, it cannot be helped but to statistically find in advance the maximum depth of flaws created, and to remove all of the detected surface flaws by as much as to the said maximum depth by the application of automatic scarfing and grinding processes. In this case, melting and grinding are often conducted to unrequired depth, to thus result in a gross metal loss. Besides, in the case of conducting removal a surface flaws in a manner of repeating the trial-and-error method for the purpose of reducing the said metal loss, considerable impairment of efficiency entails, which makes it imperative to increase the manhours for treatment of the flaws and the number of automatic flaw removal apparatuses as well, thus resulting in an increase in labor cost and equipment cost.